Influenza Activity in US Rises Slightly

Troy Brown, RN
December 05, 2018

Influenza activity in the United States rose slightly, exceeding the national baseline for the first time this season, during the week ending November 24 (week 47), according to a report from the Centers for Disease Control and Prevention (CDC).

It is still too early to tell whether the 2018-2019 season has begun, the CDC notes.

A reduction in routine healthcare visits during the Thanksgiving holidays may be partly responsible for the rise, as well as for similar increases in previous influenza seasons.

The proportion of outpatient visits for influenzalike illness (ILI) rose to 2.3% — just above the national baseline of 2.2%. Five of 10 regions reported ILI "at or above their region-specific baseline level," the CDC states.

The CDC received reports of two influenza-associated pediatric deaths during week 47, bringing the total for the 2018-2019 season to five. Both deaths were associated with influenza A viruses; the death during week 46 was linked to an influenza A(H1N1)pdm09 virus, and the one during week 47 was associated with an influenza A(H3) virus. Additionally, a 6-year-old Montana girl died from influenza B and pneumonia on December 2, according to the Missoulian.

ILI activity was high in Georgia and Louisiana and was moderate in Alabama, Oklahoma, and Utah. Activity was low in New York City, the District of Columbia, Puerto Rico, and eight states, and was minimal in 37 states.

The geographic spread of influenza was regional in Connecticut, Kentucky, Massachusetts, Oregon, and Utah; it was local in 16 states. Sporadic activity was reported in the District of Columbia, Puerto Rico, the US Virgin Islands, and 28 states. Guam and Virginia reported no influenza activity.

The proportion of deaths resulting from pneumonia and influenza during the week ending November 17 (week 46) was 5.8%, below the National Center for Health Statistics Mortality Surveillance System's epidemic threshold of 6.4%.

The Influenza Hospitalization Surveillance Network will begin reporting influenza-associated hospitalization data for the 2018-2019 influenza season later this season.

Influenza A viruses have predominated in the United States since early July, and influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B viruses continue to cocirculate during week 47. The most frequently reported influenza viruses since September 30 were influenza A(H1N1)pdm09 viruses.

Most of the influenza viruses are antigenically and genetically similar to cell-grown reference viruses representing those used in the 2018-2019 Northern Hemisphere influenza vaccines.

All influenza viruses that have been tested since late May were susceptible to the antiviral drugs oseltamivir (Tamiflu, Roche), zanamivir (Relenza, GlaxoSmithKline), and peramivir (Rapivab, BioCryst).